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* Return -- fast return in OCaml
* Copyright (C) 2008 David Teller
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version,
* with the special exception on linking described in file LICENSE.
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* Lesser General Public License for more details.
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
Local exceptions/labels/goto/return.
This module defines a mechanism akin to SML's exception generators
or to a generalization of C's [return], i.e. the ability to define
local {i labels}, which may be used for immediately terminating an
expression and returning a value. By opposition to usual OCaml
exceptions, this mechanism
- allows polymorphic return values
- makes accidental exception catching slightly harder (while a local
exception can escape its scope, it cannot be caught again by accident
from this module).
let find_in_array a e =
label (fun label ->
for i = 0 to Array.length a - 1 do
if Array.get a i = e then return label (Some i)
@author David Teller
@documents Return
type 'a t
(** A label which may be used to return values of type ['a]*)
val label : ('a t -> 'a) -> 'a
(** [label f] creates a new label [x] and invokes
[f x]. If, during the execution of [f], [return x v]
is invoked, the execution of [f x] stops
immediately and [label f] returns [v].
Otherwise, if [f x] terminates normally and
returns [y], [label f] returns [y].
Calling [return x v] from outside scope [f]
is a run-time error and causes termination
of the program.*)
val with_label : ('a t -> 'a) -> 'a
(**as [label]*)
val return : 'a t -> 'a -> _
(** Return to a label. [return l v] returns
to the point where label [l] was obtained
and produces value [l].
Calling [return l v] from outside the scope
of [l] (i.e. the call to function [label]
which produced [l]) is a run-time error
and causes termination of the program.*)
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